Materials having high refractive index (at least 1.70) in the visible spectrum are highly desired for many optical devices such as cameras, projectors, and the like. Optical elements made with high refractive indexes can be made to have higher corrective or manipulative power at a defined geometry of the lens. Therefore, refractive lenses used in optical systems can be made thinner and smaller with high-index materials. Compactness of such lenses is especially important for portable electronics such as camera phones and ultra-compact digital cameras. Various organic and inorganic high-index materials are available commercially. For example, pure TeO2 glass is known to have an index of about 2.10 at 633 nm. High index thermosetting polymers with a refractive index of 1.76 in the visible range were recently announced by Nitto Denko Corporation of Japan. However, these materials are either difficult to process, or too costly to be used in large-scale industrial production of consumer products.
High-index Sb2O3—P2O5 glasses were proposed in the prior art previously for use in optical systems. U.S. Pat. No. 5,153,151 describes moldable high-index Sb2O3—P2O5 glasses that could be used in the production of optical lenses. In order to achieve a refractive index on the order of 1.80 with this material, it was necessary to employ Sb2O3 with a content up to about 40 mol % or on the order of 65 wt %. There are concerns that pyrophosphate glasses with such high Sb2O3 levels may not have sufficient chemical durability for the desired applications. Therefore, alternative materials with comparable optical and forming characteristics but with improved water/humidity resistance are sought.
The present invention satisfies the need of such alternative high-index moldable glass.